1. Field of the Invention
The present invention relates to the uniform distribution of fluid at a distribution surface. In particular embodiments the invention relates to fluid distribution of the type occurring in separation procedures such as liquid chromatography, gas chromatography, ion exchange, distillation and absorption.
2. Description of the Prior Art
In separation procedures, particularly in liquid chromatography, the fluid distribution system is critical to the overall performance, and becomes more so as the cross-section of the chromatographic column increases.
Columns used in liquid chromatography typically comprise a body-forming structure enclosing a packing through which a carrier liquid flows, with separation taking place by material distribution between the carrier liquid and the packing. Ideally, the carrier liquid is uniformly introduced throughout the surface at the top of the column, flows through the packing at the same velocity throughout the packing cross section, and is uniformly removed at the plane defined by the bottom of the column.
Conventional distribution systems for use in liquid chromatography must address a number of inherent problems that have deleterious effects on the separation efficiency of the column. Among these problems are nonuniform initial fluid distribution at the top of the column, disruption of the surface of the bed and "channeling" within the bed.
With respect to the channeling problem, conventional distribution systems often rely upon the pressure drop in the distributor of a vertical chromatographic column to distribute the fluid uniformly horizontally. Whenever the pressure drop through the column is high relative to the pressure drop in the distributor, however, the fluid tends to channel in the center of the column causing excessive dispersion. This severely limits the effectiveness of chromatographic separations and is particularly acute for large diameter columns.
The problem of nonuniform initial fluid distribution refers generally to the problem of providing a uniform initial fluid flow at the top of the separation column. Without a uniform introduction of fluid in the plane defined by the top of the column, it is virtually impossible to achieve uniform flow distribution through the packing.
The problem of disruption of the surface of the bed stems in large part from systems that include a dead volume of fluid at the top of the column. It is desirable to have a system that permits adjustable positioning of the fluid distributor at the top of the column so that the location of the distributor can be changed with changes in column packing, thereby greatly reducing or eliminating the dead volume of fluid at the top of the column.
One well-known system for fluid distribution in liquid chromatography applications utilizes fritted discs as the distribution elements. Fritted discs are typically used in high pressure liquid chromatography (HPLC) applications wherein high pressures are used to achieve fluid distribution through the extremely small openings in the fritted discs. Such systems pose the problem of supporting the fritted discs under such pressure, particularly where the surface area of the fritted disc is comparatively large as in large-diameter column applications.
Another well-known technique for distribution is the plate system, typically utilizing a plate with face openings along radii on the plate to achieve the fluid distribution. A drawback of the plate system is that the spacing and size of the openings in the plate must be calculated for any particular fluid according to its viscosity and other physical characteristics (the rheology of the fluid) so that the system will work properly with that particular fluid at a particular flow rate. A drawback to the plate system, however, is that variation in the fluid being distributed or the flow rate will affect the uniformity of the distribution.
Despite the high level of activity in the field of chromatography over many years, and the many distribution systems proposed, both speculative as well as experimentally evaluated, the need still exists for an effective, relatively simple distribution system that will permit larger liquid chromatographic columns to be used. To date, no distribution system is available which meets this end.